IDEC SmartRelay functions
4.3 Special functions
IDEC SmartRelay Manual
126
4.3.6 Calculating the gain and offset of analog values
A sensor is connected to the analog input and converts a process variable into an electrical
signal. This value of signal lies within the typical range of this sensor.
IDEC SmartRelay always converts the electrical signals at the analog input into digital values
from 0 to 1000.
IDEC SmartRelay internally transforms a voltage of 0 V to 10 V at input AI to a range of
values from 0 to 1000. IDEC SmartRelay interprets an input voltage exceeding 10V as
internal value 1000.
Because you cannot always process the range of values from 0 to 1000 as predetermined by
IDEC SmartRelay, you can multiply the digital values by a gain factor and then shift the zero
of the range of values (offset). This allows you to output an analog value to the IDEC
SmartRelayonboard display that is proportional to the actual process variable.
Mathematical rule
Actual value
Ax =
(internal value at input Ax • gain) + offset
Gain and offset calculation
IDEC SmartRelay calculates the gain and offset based on the relevant high and low values of
the function.
Example 1:
The available thermocouples have the following technical data: -30°C to +70 °C, 0 to 10 VDC
(that is, 0 to 1000 in IDEC SmartRelay).
Actual value
= (internal value • gain) + offset, thus
-30 = (0 •A) + B, that is, offset B = -30
+70 = (1000 •A) -30, that is, gain A = 0.1
Example 2:
A pressure sensor converts a pressure of 1000 mbar into a voltage of 0 V, and a pressure of
5000 mbar into a voltage of 10 V.
Actual value
= (internal value • gain) + offset, thus
1000 = (0 •A) + B, that is, offset B = 1000
5000 = (1000 •A) +1000, that is, gain A = 4
Parameter Minimum Maximum
Input voltage (in V) 0 ≥ 10
Internal value 0 1000
Gain -10.00 +10.00
Offset -10000 +10000
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